The present invention relates to an optical driving apparatus for driving either the whole optical pickup or the objective lens of the optical pickup vertically or horizontally, for use in an optical apparatus such as an optical pickup of an optical disk player or the like, and more particularly to an optical system driving apparatus having a wide control limit.
The optical pickup of an optical disc player comprises semiconductor laser emitting a laser light, an objective lens focusing the laser light onto the optical disc, and a photodetector detecting the light reflected from the optical disc as an electronic playback signal and a control signal respectively. Such an optical disc player records information onto the optical disc, and reads the recorded information from the optical disc. Generally, this is set up to undergo coarse-seeking in the radial direction of the optical disc by an actuator such as a voice coil motor in order to access the objective lens to the target track of the optical disc. Also, the objective lens in the optical pickup is set up to undergo fine-seeking in the vertical or horizontal. direction by another actuator in order to project the light spot focused on the optical disc onto the exact center of the target track. Here, a fine-seek actuator is set up to move together with the optical pickup by means of a coarse-seek actuator (refer to U.S. Pat. Nos. 4,761,773 and 4,837,757).
In such an optical pickup, the fine-seeking actuator acts as the load of the coarse-seeking actuator, so it is desirable that the fine-seek actuator is small and light for the rapid response characteristic of the coarse-seek actuator. It is also desirable that the moving range of the fine-seek actuator is wide for a high-speed seek.
An objective lens driving apparatus of an optical disc player is disclosed in U.S Pat. No. 4,646,283. The apparatus comprises a coil having an objective lens holder connected to a base via four linear members, a coil mounted on the objective lens holder, a magnet generating magnetic flux, and a yoke constituting the magnetic path of the magnetic flux.
FIGS. 1A and 1B are schematic diagrams showing the structure of the above apparatus. That is, the right and left faces of an objective lens holder 1 are formed recessed, and edges 4a and 5a of yokes 4 and 5 to which magnets 2 and 3 are mounted, respectively, is placed in the recessed portion. A coil not shown in the drawings is wound around or mounted on objective lens holder 1 to interlink with a magnetic flux field (represented by an array of arrows) distributed between magnets 2 and 3; specifically, between edges 4a and 5a of yokes 4 and 5. In the prior art, one portion of a yoke is stretched to the inside of an objective lens holder, so that the objective lens holder occupies a lot of space and its range of fine-seeking in the horizontal direction is narrow. Therefore, the conventional apparatus has disadvantages in that the power loss of a coarse-seek actuator which coarse-seeks a fine-seeking actuator is large, and has an insufficient response characteristic due to the heavy load of an optical pickup including the fine-seek actuator. Moreover, the time required for coarse-seeking becomes overly long because the range of fine-seeking of the objective lens is narrow, which makes the apparatus unfavorable for a high-speed seeking.